The invention relates to a device for actuating a drive unit for a wiper system, in particular for a windshield wiper system of a motor vehicle. The invention also relates to a method for actuating such a drive unit.
Wiper systems for, for example, windshields of a motor vehicle, have one or more wiper arms which are provided with wiper blades in order to remove moisture in the form of precipitation or the like or water droplets from the windshield. Depending on whether and what kind of precipitation is present on the windshield, different torque values are necessary to move the wiper arms owing to the friction between the wiper blades and the surface of the windshield. The torques have to be made available during operation of the wiper arms by a corresponding drive unit for the wiper system. In particular when the wiper arms are operated on a dry window, the friction between the wiper blade and the surface of the windshield is significantly higher than in the case of a wetted surface, with the result that a high torque is necessary to move the wiper arm with a speed which is predefined by the driver.
The relatively high torque which has to be made available by the drive unit gives rise to correspondingly increased power consumption at said unit, as a result of which said unit is heated. In order to avoid damage to the drive unit due to overheating owing to a high power drain, such a drive unit is frequently protected by a thermoswitch. The thermoswitch switches the drive unit off when a predefined threshold temperature is reached or exceeded, in order to protect the drive unit of the wiper system against overheating and resulting damage. The wiping function is not available until after the drive unit has cooled down again below the threshold temperature.
Instead of the thermoswitch it is possible, in wiper motors such as, for example, reversing motors, to acquire the current temperature of the motor or the load on it by using a computational model and to switch off the corresponding drive unit if the temperature or load which is acquired in this way exceeds a corresponding threshold. However, this can lead to a situation in which a wiping function is no longer available to the driver for a certain period of time until the drive unit has correspondingly cooled down. Under certain circumstances, in the event of rain during this time sufficient visibility through the windshield cannot be ensured, as a result of which such switching off during travel can result in danger to the driver.
An object of the present invention is to make available a device for actuating a drive unit for a wiper system which provides reliable protection of the drive unit against overheating and better availability of the wiper system. An object of the present invention is also to make available a method for actuating a drive unit of a wiper system.
According to one aspect, a device for actuating a wiper system is provided. The device comprises a drive unit for driving at least one wiper arm and a control unit. The control unit is designed to set a wiping frequency of the wiper arm as a function a load variable which is dependent on a torque which is to be applied by the drive unit during a wiping operation.
The device according to the invention makes it possible to use a load variable to detect when conditions apply for an increase in temperature in the drive unit of the wiper system. As a function of the load variable, which can be acquired, for example, on the basis of actuating parameters of the drive unit, the wiping frequency or the wiping speed is correspondingly adapted in order to prevent overheating of the drive unit or an interruption in the operation of the drive unit owing to an emergency shut-down which is carried out as a function of an excessive temperature. Since an increase in the load in the drive unit is frequently caused by high friction between a dry surface of the window and the wiper blade of the wiper system, the reduction in the wiping frequency, instead of switching off the wiping, does not result in any adverse effect for the driver's vision. Adapting the wiping frequency on the basis of the load variable has the advantage that an excessive increase in temperature in the drive unit can already be avoided in advance.
Furthermore, a driver unit for actuating the drive unit and for setting a wiping frequency in accordance with a manipulated variable can be provided.
According to a further embodiment, a load variable detector is provided in order to make available the load variable as a function of the torque which is to be applied by the drive unit. In particular, the load variable detector is provided in order to determine the load variable as a function of at least one of the variables comprising the drive voltage, drive current and rotational speed which are present in the drive unit.
The control unit preferably reduces the wiping frequency of the wiper arm from a first wiping frequency to a second reduced wiping frequency if the load variable exceeds a load threshold.
Furthermore, the control unit can reduce the wiping frequency of the wiper arm after the load variable has exceeded the load threshold, after a predefined time period or after a predefined number of wiping cycles.
It is possible to provide that the control unit reduces the wiping frequency of the wiper arm to the second wiping frequency in accordance with a continuous decrease in the wiping frequency.
Furthermore, the control unit can set the first wiping frequency of the wiper arm after a second load threshold has been undershot, immediately or in accordance with a predefined continuous rise.
A switch which can be operated manually is preferably provided for setting the wiping frequency to a predefined wiping frequency independently of the wiping frequency which is set.
According to a further aspect, a method is provided for actuating a wiper system. In this connection, during the operation of a wiper arm a wiping frequency is set as a function of a torque which is to be applied for wiping with the wiper arm.